In a rotor of a synchronous motor which includes a plurality of permanent magnets for forming magnetic poles, a rotor having a rotor core assembly including a generally cylindrical rotor core formed by a lamination of thin magnetic plates and a plurality of permanent magnets arranged and affixed on the periphery of the rotor core at predetermined pitches in a circumferential direction, is known. In this type of rotor, a magnetizing process of the permanent magnets has been generally performed for each of a simple permanent magnet material, individually, before incorporating the same into the rotor core, or for all permanent magnet materials after affixing them at predetermined positions on the rotor core.
However, these conventional methods of magnetizing have had problems as described below when the electric motor must be increased in size. First, in the method of magnetizing a simple permanent magnet material, since the size of the permanent magnet material is also increased following the scaling up of a motor, it becomes difficult to correctly affix large and heavy permanent magnets at predetermined positions on a rotor core when the permanent magnets are affixed to the rotor core after being magnetized, and this problem is increased by the repelling magnetic force between the adjoining magnets. Further, in the method of magnetizing all permanent magnet materials after affixing them on the rotor core, a large-size magnetizer becomes necessary in accordance with the scaling up of the motor, and manufacture of such a magnetizer would not be easy. Accordingly, the method may be considered of using a relatively small normal magnetizer for magnetizing the same pole part of the permanent magnet materials affixed on the rotor core and repeating this to magnetize the overall magnet materials, but this method is not desirable since the leakage flux will have a detrimental effect on the magnets other than the magnetized part during the magnetization of each part.